DLPlat BAGold,
What you are asking is not called an "endorse," but it is called "re-routing." You do know that what you're asking is not the same as asking for say switching from CX to BA for HKG-LHR, right?
May I kindly ask what exactly is your intention of the re-routing from HKG-(x/YVR)-JFK to HKG-x/SYD-(x/LAX)-JFK?